The present invention relates to a new and improved process for the production of sterile yoghurt, wherein milk is pasteurized and homogenized and, furthermore concentrated by 10% by weight at a temperature of about 92.degree.C, thereafter there is added 10% to 12% by weight sugar, cooled to about 40.degree.C and through the addition of cultures of lactic acid bacteria acidified to a pH-value of 4.0 to 4.3, by incubation over 21/2 to 4 hours at a temperature in the range of 42.degree.C to 44.degree.C and after incubation cooled to a temperature in the order of 20.degree.C to 30.degree.C.
The sterile yoghurt produced according to the invention is absolutely free of bacteria or germs and without cooling can be stored up to six months without decomposition occurring or losing its typical taste or the consistency thereof changing. Preferably yoghurt with fruit aromas are produced according to the inventive process, yet the yoghurt can possess other tastes, such as for instance hazel nut aroma.
It is generally known that yoghurt is a product formed of heated milk with specific fermentation promoters, containing a minimum fat content in accordance with the regulated milk, and the dry mass of which can be increased by the vaporization or addition of dried or powder milk or low-fat or skimmed dried milk. Yoghurt is a curdled or acidic milk which is frequently drunk in the Balkan countries, for instance Bulgaria, and which differs from conventional curdled milk due to the nature of the microorganisms. Yoghurt primarily contains Lactobacillus yoghurt, Lactobacillus bulgaricus and Streptococcus thermophilus, whereas the curdling of the conventional milk is brought about by Bacteria (lactis) aerogenis Streptococcus lacticus and the like.
Heretofore known prior art processes for the manufacture of yoghurt are carried out in the following manner
The milk from a cow is vaporized until reaching approximately a specific weight of 1.035 (or there is added skimmed dried or powdered milk), then rapidly cooled from a temperature range of about 95.degree.C to 97.degree.C to a temperature range of 42.degree.C to 45.degree.C and there is added thereto 4% to 6% of the above-mentioned bacteria culture. The entire mass or mixture is then maintained for 2 1/2 to 3 hours at a temperature of 42.degree.C to 45.degree.C (water bath, cooking vessel, incubator), whereby a portion of the sugar of milk or lactose is transformed by bacteria into lactic acid and some alcohol and there then occurs coagulation or curdling. Finally, the yoghurt is filled into small carefully incubated vessels or containers, stored 1 to 1 1/2 hours at room temperature, cooled in a stream of cold water and stored for at least 5 hours at 4.degree.C to 5.degree.C. A process proposed in Czechoslovakia recommends heating to 52.degree. C for 30 minutes and then cooling for a short time to 20.degree.C to 21.degree.C. In this regard attention is invited to the publication "Food Manufacture 1963", page 176. In U.S. Pat. No. 3,025,165, there is obtained from milk where the cream has been skimmed, yoghurt free of butter, which after dispersing of highly unsaturated oils or fats has added thereto in conventional manner yoghurt bacteria. The addition of fruits or other aromatic substances occurs prior to filling into the containers. Yoghurt before it is edible should be at least 12 hours old and at least have been stored for 5 hours at 4.degree.C to 6.degree.C. It is especially recommended for persons suffering from stomach and intestinal problems; its lactic acid is supposed to counteract damaging intestinal bacteria. According to the article of Baumgartel, appearing in the publication "Vitalstoffe" 1959, pages 193-198, the Escherichia colibacteria are displaced by the yoghurt, with the result that there is quite markedly intensified the acidophilus bacteria in the intestine; the same effect is attained by acidophilus preparations. The lactic acid content of yoghurt should not be less than 0.8% and should not amount to much more than 1.0%. Each 100 grams yoghurt contains on the average 86.1 grams water, 4.8 grams protein, 3.75 grams fat, 4.5 grams carbohydrate, 0.86 grams mineral substances, 42 mg.Na, 190 mg.K, 150 mg.Ca, 135 mg.P, 0.033 mg.vitamin A, 0.045mg.vitamin B.sub.1, 0.24 mg.vitamin B.sub.2, and 2 mg.vitamin C.
Yoghurt produced according to conventional processes only can be stored while cooled and transported to a limited extent. Since the yoghurt heretofore known still contains bacteria, in particular Streptococcus thermophilus, there also can occur the formation of carbonic acid, apart from the formation of mildew and other decomposition products.